Why do I have so many pimples on the shaft of my ?

Okay, so, I'm 15 and there are many, many, MANY pimples on the shaft of my . I'm pretty sure they're not Pearly Penile Papules but they're filled with pus. Some of them are hair follicles but most aren't and I'm not sure what to do at the moment. I'm thinking that they may be from masturbating because, like most teenagers, I masturbate pretty much once or more a day. Any help would be greatly appreciated.